Choucas, a former police detective, is commissioned by an elderly lady to investigate the disappearance of her blind daughter, Marthe. The lady is murdered. Assisted by retired commissioner Haymann, and by secretary Charlotte, investigator Choucas attempts to unravel the thread of a fraud involving various police services and drug traffickers. During the investigation Choucas is attacked in the apartment of the victim by a certain Pradier; he kills him but his accomplice manages to escape. Back home, Choucas escapes an ambush tended by a certain commissioner Madrier and kills him, with the result of ending up in the viewfinder not only of a mysterious gang, but also of the police.